1. Field of the Invention
The present invention relates to an aligning unit for aligning transfer materials after printing and an image forming apparatus such as a copier, a printer or a facsimile machine provided with such an aligning unit.
2. Description of the Related Art
In an image forming apparatus, stapling of binding a plurality of transfer materials into a bunch, perforation or like post-processing is sometimes applied to transfer materials (paper sheets, resin films, etc.) after printing. For such a post-processing, image forming apparatuses have been conventionally proposed which are each provided with an aligning unit constructed such that a plurality of transfer materials (e.g. paper sheets, resin films) discharged to a tray defined in a main body of the image forming apparatus (called as an intermediate tray below in order to be distinguished from a discharge tray to be described later) are aligned, a resulting bunch of the transfer materials is moved to a post-processing position, and the bunch of the transfer materials after the post-processing is moved from the intermediate tray to a specified position to be discharged to a discharge tray (see, for example, Japanese Unexamined Patent Publication No. 2002-68578).
Such an aligning unit stacks the printed transfer materials discharged on the intermediate tray while positioning them with respect to forward and backward directions and transverse directions. The aligning unit includes restricting members opposed to each other. While one restricting member restricts the transfer materials at one end, the other restricting member is slid to restrict the transfer materials at the other end, thereby aligning the transfer materials. Thereafter, the aligned transfer materials are moved to the post-processing position for post processing such as stapling.
Here, in the case of, e.g. thermally fixing a toner image to the transfer material, an end portion of the transfer material discharged onto the intermediate tray is, in some cases, largely curled upward depending on the material of the transfer material, a hygroscopic state thereof or the like. If the transfer material is curled in such a way, it might not be aligned to a correct position upon being positioned.
A known construction taking such a problem into consideration is such that an oblique wall inclined toward the opposed restricting member as it extends from a placing surface of the intermediate tray toward the upper end is formed atop the slidable restricting member (see, for example, Japanese Unexamined Patent Publication No. 2002-114433). By this construction, the transfer material placed on the intermediate tray can be suitably aligned even if it is curled upward.
However, the above construction has a problem that the transfer material cannot be properly aligned if it is curled downward. Further, in a mode of performing alignment (sliding movement of the restricting member) every time one transfer material is conveyed, if only the conveyed transfer material is displaced from an alignment position when one transfer material is conveyed anew to the intermediate tray already bearing a plurality of transfer materials thereon, a part of the transfer material displaced from the alignment position is locally curled downward (hangs down) depending on the material of the transfer material. If alignment is performed in this state, the newly conveyed transfer material is sandwiched between the restricting member and the plurality of transfer materials placed (already aligned) at the alignment position and might be buckled.